The present invention relates to a device and to a method which allow a surgeon, when implanting a total endoprosthetic knee joint, to execute resection of the femur and of the tibia in an extremely precise manner.
The exact position of the resection lines on femur and tibia is of crucial importance for a long useful life of a total endoprosthetic knee joint. To date, resection has been extremely demanding, even for an experienced surgeon, since it is necessary, by means of the operation, to create the normal bearing surfaces according to the predetermined geometry of the endoprosthesis, in so doing to align the normal bearing surfaces according to the desired mechanical leg axes, if appropriate also correcting pathological defects of position, and in addition to take into account the position and the effect of the ligaments and muscles which are present. The alignment of tibia and femur is usually carried out by visual examination with the possible use of intramedullary or extramedullary aids, in which case an additional problem is that access to the operating field is often made difficult. These marginal circumstances can cause stressful situations even for surgeons with considerable experience.
A total endoprosthetic knee joint consists of a component secured to the femur and of a component secured to the tibia. Before the total endoprosthetic knee joint can be implanted, the adjoining bone areas of the femur and of the tibia must be appropriately resected in order to create normal bearing surfaces corresponding to the geometry of the endoprostheses. The frontal surfaces of the tibia and of the femur are usually resected. At least the femur is additionally provided with a so-called dorsal cut and a ventral cut since the femoral part of total endoprostheses is usually unshaped. The instruments generally supplied by manufacturers of prosthetic knees do not allow the necessary bone cuts on femur and tibia to be made with the required precision.
A further important requirement, however, is to ensure that those components of the prosthetic knee which slide on each other during flexion and extension of the knee are always in the correct position relative to each other, i.e. that the mechanical leg axis can deviate by not more than 3xc2x0 varus or 3xc2x0 valgus from the physiological bone axis, the deviation preferably being less than xc2x12xc2x0. In addition, it must also be borne in mind that the flexible connection between the two components is caused by ligaments and muscles, insofar as these are preserved upon implantation of the prosthesis. This requires equilibration of the ligament apparatus, ensuring good stability of the knee joint both in extension and in flexion.
The known instruments for implantation of total endoprosthetic knee joints generally comprise the following means:
means for aligning the tibia relative to the femur in order to obtain the desired leg axis position;
means for producing the desired tensioning of the knee ligaments;
means for performing resection of tibia and femur, in the form of sawing jigs which serve to guide a saw blade.
Such an instrument is known from the printed specification EP 0 322 363 A1. This instrument uses an extramedullary means for alignment of tibia and femur (extramedullary alignment system) and has the disadvantage that the alignment of the femur can be determined only with the aid of an X-ray apparatus. In addition, the reference system for the bone cuts is put in place by sight, said reference system additionally making access to the operating field difficult.
A further instrument is known from the printed specification EP 0 691 110 A2. This instrument uses an intramedullary means for alignment of tibia and femur (intramedullary alignment system) and has the disadvantage that a guide bar is in each case needed for mutual fixation of tibia and femur, said guide bar being introduced into medullary space of the tibia and femur, respectively. This intervention in the medullary space can cause thromboses and embolisms, with a possibly fatal outcome.
The object of the present invention is to make available a device and a method for localizing resection cuts on the femur and on the tibia for preparing an implantation of a total endoprosthetic knee joint, which method can be performed easily and in a reliably reproducible manner.
This object is achieved with a device having the features of claim 1, 15 or 23. The dependent claims 2 to 14, 16 to 22, and 24 to 36, relate to further advantageous embodiments of the device according to the invention. The object is also achieved with a method having the features of claim 37.
In an advantageous embodiment, the device according to the invention comprises a reference device consisting essentially of a base part which can be detachably locked in the distal area of the femur and of a reference body which is connected to the base part in an articulated and/or displaceable manner, which reference body has means defining a system of coordinates X, Y, Z, where the alignment of the reference body can be accurately positioned relative to the femur and where an actuating means acting between the reference body and the base part is provided for fixing the mutual position thereof, and where the means defining the system of coordinates X, Y, Z are designed for aligned attachment of working means such as a sawing jig, a base bar or a measurement device.
An advantage of this device is that the reference device is connected securely to the femur and is preferably aligned in the direction of extent of the weight-bearing axis of the femur, and that all the cuts on femur and tibia are carried out aligned relative to this reference system so that resection cuts or resection surfaces can be formed on the femur and tibia with very great precision and in a defined alignment.
The reference device can be secured on the femur by a large number of differently designed means, for example with bone screws, or with gripper arms which at least partially enclose the femur and can additionally have spikes which penetrate into the femur for improved anchoring.
In another advantageous embodiment, the device according to the invention comprises a reference device which can be secured extramedullarly and detachably in the distal area of the femur and whose alignment can be accurately positioned relative to the femur, and comprising a tibial splint which can be secured extramedullarly and detachably on the tibia, where the alignment of the tibial splint can be accurately positioned relative to the tibia, and comprising a securing device which securely connects the reference device and the tibial splint in a detachable manner.
This embodiment according to the invention has the advantage that the tibia can be brought into a precisely defined position relative to the femur and can then be fixed in this position. The direction of extent of the resection cuts on the tibia can therefore be predetermined by the cutting device secured on the femur. The position of the tibia can be accurately adjusted relative to the femur, for example in order to correct the line of the mechanical leg axis. In one advantageous embodiment, the securing device is of U-shaped or rectangular design, so that the operating area on the knee is by and large freely accessible even when the securing device is in place.
In a further advantageous embodiment, the device according to the invention comprises a reference device which can be detachably locked on the distal area of the femur and whose alignment can be accurately positioned relative to the femur, and a cutting device which is movably connected to the reference device, in particular a sawing jig for guiding a saw blade, or a sawing device having a saw blade, where the alignment of the cutting device, in particular of the saw blade, is determined at least by the alignment of the reference device. It is possible to use cutting devices with very different cutting methods, for example saws, ultrasonic cutting devices, or use of lasers. The device according to the invention allows the cutting device to be guided in such a way that the cut extends in the intended direction. An advantageous method for generating the cut has proven to be the use of a saw.
In a particularly advantageous embodiment, the sawing device comprises a saw blade whose extent defines a saw blade plane, the sawing device being secured with a connection means on the reference device and on the adjustment device, and the connection means and the sawing device being designed in such a way that the saw blade is mounted so as to be displaceable exclusively in the saw blade plane.
This embodiment has the advantage that the alignment of the saw blade is predetermined so that the operating surgeon can concentrate exclusively on moving the saw blade toward the bone and executing the resection, in the certainty that the alignment of the resection plane is correct. This makes things considerably easier for the operating surgeon during resection since he can concentrate essentially on the cutting, and in so doing can concentrate on any obstacles such as ligaments, and without having to worry about the direction of extent of the saw.
The device according to the invention can also be driven by a motor. In addition, a computer can be provided which monitors or even controls the movement of the device and the cutting.
The method according to the invention for performing resection cuts on femur or tibia is carried out in particular by means of a reference device being fixed on the distal area of the femur and then aligned relative to the direction of extent of the femur, and by means of a sawing jig, for guiding a saw blade, or a sawing device with a saw blade, being connected displaceably to the aligned reference device and being guided in an alignment defining the direction of extent of the resection cut, and by means of the resection being performed with the saw blade guided in alignment.